feat(deploy): serve SPA from server, Dockerfile, compose, deploy docs

- Add serveStatic middleware to server/src/app.ts to serve web/dist
- Include SPA fallback route for client-side routing deep links
- Create Dockerfile with multi-stage build (Node deps + build, slim runtime)
- Add docker-compose.yml for single-command deployment
- Add docs/deploy.md with deployment instructions and Caddy reverse proxy example
- Add bun run build:web step to CI pipeline after typecheck

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/deploy.md

@@ -0,0 +1,17 @@
+# Deploying Helios
+
+    git clone https://git.rehbock.xyz/marcus/helios.git && cd helios
+    docker compose up -d
+
+Open http://your-host:3000 and create the instance password.
+
+Back up the `./data` directory — it holds the SQLite DB, uploads, and
+`secret.key`. Without `secret.key` your stored API keys are unrecoverable.
+Run the host disk encrypted; Helios encrypts credentials column-level but
+not the whole DB file.
+
+## Reverse proxy (Caddy)
+
+    helios.example.com {
+        reverse_proxy localhost:3000
+    }